Collision warning and intelligent cruise control systems generally employ a forward looking radar, laser or ultrasonic sensor (FLS) mounted at the forward end of the host vehicle for acquiring data corresponding to the range, range rate, and the azimuth angle of a target vehicle or other object. The range is the distance between the host vehicle and the target, the range rate is the rate of change of range, and the azimuth angle is the angle in a horizontal plane between the target and the direction of travel (the path or trajectory) of the host vehicle. A microprocessor receives and analyzes the sensor data along with other data corresponding to the vehicle velocity and yaw rate and/or lateral acceleration, and predicts the likelihood of an impending collision. In a collision warning system, the primary function of the system is to warn the operator of a potentially unsafe operating condition, or possibly to initiate a corrective action, whereas in an intelligent cruise control system, the primary function is to adjust the vehicle speed to maintain a desired headway or following distance. Such systems require an accurate determination of the target location relative to the path of travel of the host vehicle. This, in turn, requires precise alignment of the FLS viewing axis, and accurate detection of the yaw or lateral acceleration of the host vehicle.
In practice, precise alignment of the FLS sensor is difficult to achieve in a factory environment, and even more difficult to maintain in subsequent usage of the vehicle due to changes in wheel alignment, for example. Additionally, yaw or lateral acceleration sensors which are used to determine the travel path radius of curvature typically exhibit a certain amount of temperature-related drift. Even when differential wheel speeds are used to estimate travel path curvature, differences in tire pressure and wear, or road surface variations, can introduce significant error. As a result, it is difficult to accurately assess if a detected target is in the travel path of the host vehicle.